Calibration of the State Space Thermal Model of a Directly Cooled Permanent Magnet Synchronous Machine

The strive for higher power densities in electrical machines due to spatial and weight specifications implicates the need of enhanced cooling methods to dissipate the loss related heat. An effective approach to meet these demands is cooling the stator winding directly, i.e. the coils are in direct contact with the cooling fluid. In addition, a non-conductive tube installed in the airgap keeps the rotor dry and thus prevents additional churning or eddy current losses. This paper focuses on thermal aspects of such a directly cooled permanent magnet synchronous machine. Therefore, a lumped parameter thermal network in state space representation is derived, offering a real-time capable solution to compute the temperature in the respective machine components. Furthermore, a new methodology for parameter identification is proposed, which exploits the final value theorem for state-space systems to extract the heat transfer coefficients from thermal machine measurements. Both thermal modeling and parameter identification are finally validated by experiment.